1. Field of the Invention
The present invention relates to medical devices, for example, radiotherapy apparatuses and CT (computed tomography) apparatuses.
2. Description of Related Art
Stereotactic radiotherapy apparatuses are known medical devices for treating affected areas such as tumors by irradiating them with radiation (therapeutic radiation). In such stereotactic radiotherapy apparatuses, the same affected area is irradiated multiple times with radiation from multiple directions. In order to irradiate radiation from multiple directions, it is necessary to provide a radiation emitter which can be moved to and aligned at multiple positions around the patient and which is disposed at a position corresponding to the point where radiation for irradiating the affected area is to be emitted. Known approaches for moving the radiation emitter in this way include the cantilever type, robotic arm type, and gantry type approaches.
In the cantilever type approach, the radiation emitter is supported in a cantilevered manner and rotated around the patient's body. In the robotic arm type approach, the radiation emitter is attached to the end of a multi-axis arm, and the radiation (therapeutic radiation) is radiated from an arbitrary direction. However, with the cantilever type approach or the robotic arm type approach, because of the structure wherein the radiation emitter is attached to the end of the cantilever beam or the arm, the cantilever beam or the arm becomes deformed due to the weight of the radiation emitter, thus making high-precision positioning (irradiation direction setting) difficult.
In contrast, in the gantry type approach, a gantry is positioned so as to surround a patient lying on a couch, and the radiation emitter is moved along the gantry or together with the gantry. The gantry type approach is preferable for realizing high-precision positioning because the radiation emitter is supported by a highly rigid gate-shaped gantry. Medical devices using this gantry type approach have been disclosed, for example, in Japanese Translation of PCT International Application, Publication No. HEI-8-511452 and PCT International Publication No. WO2003/018132 Pamphlet.
With the cantilever type approach and the gantry type approach, in order to increase the degree of freedom of the irradiation direction, positioning control of the couch on which the patient is set (translation and rotation) is performed, in addition to translation of the radiation emitter in a single direction.
Japanese Translation of PCT International Application, Publication No. HEI-8-511452 discloses a radiotherapy apparatus in which a ring-shaped gantry is accommodated inside a radiation barrier, also serving as a housing, and a radiation emitter is provided on the gantry, as shown in FIG. 2 of that publication. In this radiotherapy apparatus, the radiation emitter is rotated by rotating the gantry inside the radiation barrier.
PCT International Publication No. WO2003/018132 Pamphlet discloses a radiotherapy apparatus including a ring-shaped guide, a ring-shaped movable member attached at the inner side of the guide, and a radiation emitter provided on the movable member, as shown in FIGS. 13 to 16 of that publication. In this radiotherapy apparatus, the radiation emitter is rotated by rotating the movable member along the guide.